In the prior art a damper is known comprising a cylinder provided with a first attachment means and a piston which can be displaced therein and which is fitted on a hollow piston rod with a second attachment means, wherein said cylinder is divided into a first chamber and a second chamber by said piston, wherein a passage for damping fluid from the second chamber to said first chamber is present, in which passage a first main non-return valve limiting the flow of damping fluid is present, wherein said second chamber comprises the bottom of said cylinder, wherein a liquid reservoir is present which is in fluid connection with said second chamber, wherein a non-return valve is present in said fluid connection and blocks the flow from said second chamber to said liquid reservoir, a sleeve extends from said bottom, which sleeve is in fluid communication with said liquid reservoir and wherein a connection from said first chamber to said cavity via the piston is present downstream of said first main non-return valve when the piston is moved to the bottom of said cylinder.
A damper of this type is suitable for many applications, one of which is the use in railway applications and, more particularly, in attenuating the rotating movement of a wheel set with respect to the carriage body. Particularly with railway carriages travelling at high speeds, it is important to effectively attenuate the slight mutual movements between the wheel set and the carriage body at high speeds. To this end, it is important that the damper which is used is relatively stiff at high frequencies (such as from 6-8 Hz) and low speeds, that is to say that there is as little gas as possible present in the hydraulic fluid used.
GB 2,159,604 discloses an adjustable hydraulic damper which can be used for entirely different applications.